Chemistry Reference
In-Depth Information
the reactor by means of a piston pump and a lamellar vaporizer. All liquids were care-
fully degassed. Monomer fluxes were measured by mass flow controllers.
2.2. Surface analysis
The XPS data acquisition was performed with a SAGE 150 Spectrometer (Specs,
Berlin, Germany) using non-monochromatized MgK
α
or AlK
α
radiation with 12.5
kV and 250 W settings at a pressure 10
7
Pa in the analysis chamber. This instru-
ment is equipped with a plasma reactor separated by a gate valve from the UHV
system, where surface treatments can be carried out at 10
1
-10
-7
Pa. XPS spectra
were acquired in the constant analyser energy (CAE) mode at 90° take-off angle.
Peak analysis was performed using the peak fit routine from Specs.
Near Edge X-ray Absorption Fine Structure (NEXAFS) and XPS measure-
ments on
in situ
plasma treated surfaces have been described in detail elsewhere
[31-33]. The plasma polymerisation was performed in a UHV preparation cham-
ber connected to the spectrometer. The FTIR spectra were recorded with a Magna
550 instrument (Nicolet, USA) using the ATR technique with Ge crystals or a
diamond cell (Specac, Kent, UK). IR-GIR (Grazing Incidence Reflectance) meas-
urements were performed on a GIR unit (Specac, Kent, UK) where the angle of
incidence was variable. Most often these IR measurements were made at an angle
of incidence of 70°. The GIR method was convenient and helped us to avoid in-
fluences of moisture, as shown by parallel measurements with plasma polymer
layers on KBr or NaCl.
2.3. Analysis of plasma polymer layers
2.3.1. ThFFF analysis
Molecular masses higher than ca. 500,000 Da and their distribution were deter-
mined by Thermal Field Flow Fractionation (ThFFF, for details see [34]). Addi-
tionally, slightly crosslinked polymer particles (gels) with the radius of gyration
up to ca. 100 µm were analysed. This range of radii corresponds to molar masses
of 10
5
to
10
12
Da. The separation principle is based on the different thermal dif-
fusion behaviours of molecules and particles between a high temperature gradient.
One side of the channel is heated up to 150°C and the other side is cooled. It was
possible to analyse all pulsed plasma polymerised vinyl, acrylic and allyl mono-
mers without filtering. A ThFFF apparatus supplied by Wyatt Technology (Ham-
burg, Germany) including Refractive Index (RI), UV, and Multi-Angle Laser
Light Scattering (MALLS) detectors as well as an Evaporative Light Scattering
Detector (ELSD) was used in these experiments.
2.3.2. AFFFF analysis
In contrast to the separation mechanism used in ThFFF, the Asymmetric Flow Field
Flow Fractionation (AF
4
, also called Crossflow FFF) uses a (second) cross flow of
the solvent. Particles, suspensions, colloids/gels and molecules up to 100 µm in di-
ameter are separated. Due to the cross flow through a membrane, low-molar mass
≥
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